IoT as a Crack Monitoring Tool

The technology, used in the monitoring of structures, makes it possible to avoid in the construction industry the risks of subsidence linked to the development of cracks.

A dozen electronic crack sensors and around forty mechanical gauges from the French company Feelbat have been fitted to the Piton Maïdo fault in Reunion since the beginning of April 2022 to monitor the cracks. Similarly, a series of crack and settlement sensors and inclinometers from the French company Socotec Monitoring, developer and integrator of sensors, will instrument the Madeleine church in Paris next June for the same purpose. In the construction industry, the IoT affirms its value in monitoring cracks, in particular to predict any risk of building collapse.

This monitoring of cracks has been at stake “for a long time, but the use of the IoT for this diagnostic use is new”, notes Yassine Chafiq, deputy general manager at Socotec Monitoring. The reason ? “The instrumentation was already existing with wired processes to transmit a lot of data. The manufacturers of these devices had never before developed them in IoT, because wireless sensors are more constrained (by data size, editor’s note) with this technology in the transmission of information”, he explains. New offers are nevertheless emerging. “The IoT was becoming essential because the monitoring of certain structures by wired boxes a PC to configure them was unmanageable”, assures Jean-Christophe Habot, founder of Feelbat. The latter developed his own three ranges of Delta plug and play sensors in Sigfox less than two years ago. Result: he succeeded to attract a hundred customers in less than six months, from its launch in December 2021, and specializes in consulting.

20,000 IoT sensors for Greater Paris

Sensors are installed at regular intervals along the 45 km of railway tracks of the Grand Paris site. © Socotec

One of the sector’s flagship projects concerns Greater Paris, a long-term project representing for Socotec Monitoring 45 kilometers of railways and 13 tunnels to be monitored, by some 20,000 IoT sensors installed. “We have been instrumenting it since 2017, having started with line 15 then line 16. The work is progressing gradually with temporary phases, hence the need for wireless IoT. We must ensure that the digging of the tunnel does not causes no risk of subsidence or tilting of buildings around its axis”, explains Yassine Chafiq.

These crack sensors, generally IP66-rated to resist humidity, are characterized by their high accuracy. “They integrate robust technologies. Our mechanical gauge, for example, studies cracks on three axes, the walls are monitored in real time on the application according to their movements and their temperature. (one of the parameters causing a crack, editor’s note)“, says Jean-Christophe Habot. For their part, the orders of magnitude in terms of precision for the vibrating wire of Socotec Monitoring is micrometers per meter, and on the LoRa inclination sensor 0.005 degrees of precision.

“Often, customers save these costs in prevention and call us once the crack is already there”

The challenge for these players is to further democratize the cost of sensors to make them accessible during all work. For example, Socotec Monitoring, which targets major structures, sells its sensors for around 700 euros, a variable and tailor-made price depending on capacities and projects. Feelbat, which mainly targets small communities, has chosen to market them at 299 euros for its electronic sensor and 399 euros for its tilt sensor in order to be sure that its customers install enough of them on a construction site. “It is better to ask more to monitor work. Often, customers save these prevention monitoring costs and call us once the crack is already there”, notes Jean-Christophe Habot with regret.

For Socotec Monitoring, which is currently developing a LoRa acquisition module for the vibrating wire strain sensor for infrastructures, the market prospects are enormous with the development of tunnels, offshore wind platforms and constructions for the 2024 Olympic Games. An opinion shared by Feelback, which for its part targets buildings and small works of art with little supervision. “Technology is not limited to large infrastructures, you also have to monitor homes, as soon as you do work at home to limit the risks to your neighbours”, recalls Jean-Christophe Habot, citing as an example the balconies of building that collapsed in Bordeaux and Marseille. In the Netherlands, it is a legislative obligation to instrument its work, for example the digging of a swimming pool. The technology applied to crack monitoring, so far focused on BtoB, could eventually become a BtoC solution with instruments indicated as part of its smart home.

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